Septic Tanks and Treatment Plants
For homes that have poor drainage or are not connected to the mains sewage network septic tanks allow a safe disposal of waste water. They work by collecting the excreta and wastewater in one big underground tank and they are predominantly used in rural areas.
A sewage treatment plant provides treatment of the waste, whereas a septic tank simply separates it - this means that the waste water that leaves a sewage treatment plant is cleaner than what leaves a septic tank. You still might not want to brush your teeth with it, but it's certainly a lot more environmentally friendly.